Wave propagation in composite conductors



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A TTOR/VE V United States Patent j O l WAVE PROPAGATION [N COMPOSITECONDUCTORS Application May 5l, 1951, Serial No. 224,778 14 Claims. (Cl.S33-27) This invention relates to electromagnetic wave propagatingsystems and more particularly to systems using composite conductorsformed of a multiplicity of elongated insulated conducting portions.

It is an object of this invention to provide apparatus for exciting `andutilizing electromagnetic waves propagating in modes of higher orderthan the principal or dominant one in electrical conductors of thecomposite type, such as, for example, in one of the types shown anddescribed in the copending application of A. M. Clogston, Serial No.214,393, `filed March 7, 1951. In the present application, the termInode is used to indicate a space pattern of fan electromagnetic field,current or voltage. j

In the above-mentioned application of A. M. Clogston, there aredisclosed a number of composite conductors each of which comprises 'amultiplicity of insulated conducting elements of such number, dimensionsfand disposition relative to each other and the orientation of theelectromagnetic wave being propagated therein as to achieve a morefavorable distribution of current and eld within the conductingmaterial. In one specific exemplary embodiment disclosed in Figs. 7A and7B of the Clogston application, a plurality of coaxially arrangedcylindrical composite conductors are separated by a dielectric material,each of the composite conductors comprising a multiplicity of thin metallamjnations insulated from one another by layers `of insulatingmaterial, the smallest dimension of the laminations being in thedirection perpendicular to both the direction of wave propagation andthe magnetic vector. Each metal lamination is many times (for example,10, 100, or even 1000 times) smaller than a factor which is called oneskin depth. This distance is given by the expression:

ma where is the skin depth expressed in meters, f is the frequency incycles per second, p. is the permeability of the met-al in henries permeter, and a is the conductivity in mhos per meter. This factor measuresthe distance in which the current or field penetrating into a slab ofthe metal many times in thickness will decrease by one neper; i. e.,their amplitudes will become equal to times their amplitudes at thesurface of the slab.

It was pointed out in the Clogston application that when a conductor hassuch a laminated structure, a wave propagated along the conductor at avelocity in the neighborhood of a certain critical value will penetratefurther into the conductor (or completely through it) than it wouldpenetrate into a solid conductor of the same material, resulting in amore uniform current distribution in the laminated conductor andconsequently lower losses. The critical velocity for the type ofstructure just described is determined by the thickness of the metal andinsulating laminae and the dielectric constant of the insulation betweenthe metal laminae in the Y 2,769,147 Patented Oct. 30, 1956 ricecomposite conductors. The critical velocity can be maintained by makingthe dielectric constant of the main dielectric i. e., the dielectricm-aterial between the two composite conductors, equal to where e, is thedielectric constant of the main dielectric element between the twocomposite conductors in farads per meter, e, is the -dielectric constantof the insulating material between the laminae of the conductors in farflads per meter, W is the thickness of one of the metal laminae in metersand t is the thickness of an insulating layer in meters. The insulatinglayers are also made very thin Aand an optimum thicknessfor certainstructures of this generaltype is that in which each insulating layer isone-half of the thickness of a metal lamina. It can beiseen fromEquation 2 that the expression is actually the average transversedielectric constant of thelarninated medium. Since, as pointed out inthe aforementioned Clogst-ron application, the velocity of propagationof an electromagnetic wave in a medium is proportional to where trepresents the permeability of the medium and e represents thedielectric constant, the velocity is the same in two diiferent media ifthe product of ,ue is the same for the two media, all else being lequal.If the two media are adjacent each other, the velocity of propagation issubstantially uniform throughout the crosssection of the area defined bythe two media.

The present invention relates to the use of such a composite structureof the type just described in combination with apparatus for excitingand utilizing therein electromagnetic waves of higher order conductioncurrent modes as distinguished from dielectric wave guide modes, andalso to the excitation and utilization of such conduc-` tion currentmodes in other related composite conductor structures, such as, forexample, others described in the above-mentioned Clogston application.As hereinafter used in" the specification and claims, the termconduction current mode designates electromagnetic wave modes of thetype wherein there is a variation in the current distribution patternacross the conductor as well as a variation in eld pattern for thediierent modes. These modes differ from the more familiar wave guide`modes which exhibit diierences in field patterns for the i (2) inconnection with a variation which is shownin Fig.

17A of the above-rnentioned Clogston application and` which is similarto the embodiment just described in detail except for the fact that thedielectric member between the two composite conductors is` completelyiilled with alternate metal and insulating laminae, thus forming inessence one large cylindrical stack of insulated metal laminae, and (3)in connectionwith la variation of these embodiments in which amultiplicity of tiny elongated iilaments are used in place of the metallaminae and which is described in greater detail -in connection withFigs. 18A and 18B of the above-mentioned Clogvs ton application. lt willbe understood, however, and clearly obvious to one skilled in the art,that the invention is not limited to combinations utilizing theabovementioned specific structures since it can be readily -applied toother structures of the composite type men- ;tionedin theaboVe-identiiied Clogston application and to other modificationsemploying the same principles. In any of the composite conductorsdescribed above, there exist a multiplicity of modes of transmission inwhich the fundamental, principal or dominant mode with propagationconstant ko corresponds to the lordinary mode of. transmission thatwould exist between a pair of parallel Vspaced plates. The higher modesare waves that are conned. almost entirely to the laminations (orlaments) andare not encountered in an ordinary transmission line.",Ilieyhave many interesting properties. The waves propagating in allVthe modes travel at nearly the same speed andmay include waves down tozero frequency. The highest frequency which can be transmitted, however,increases as the mode number increases. Moreover, the attenuation of.the waves increases as the mode number increases. By way of example,the second order mode has an attenuation much greater than that of thefundamental mode, the attenuation of the third order mode isagaingre'ater than that of the second order modes, and Vthe attenuationof the fourth order mode is still greater than that 'of the third ordermode. In the description that followsfit will'bepointed out' how variousmodes can be excited and utilized in a composite conductor to theexclusion of other modes and also an arrangement will be shown anddescribed in which waves operating in a plurality of modes areindependently and simultaneously propagatedand utilized in compositeconductor systems. The invention wilfbe more readily understood byIfferring to the yfollowing description taken in connection wit:the,acco'rr'ipanyingl drawings forming a part thereof, in Which W Fig."l'is a longtiudinal View, with portions broken WY, of a coaxialtransmission line of the type shown inA fFi 7B,l of the above-mentionedClogston application f 'which waves of various modes are excited in ance:withthe invention; f lA to "1E," inclus/ive, show approximate currentdensitypatterns, ofthefundamental, second, third, fourth a` odes.,respectively, in a transmission line of shw'niFigfl'; i' Y "`Fi g. 2 isYa longitudinal view, with portions broken away, of Va coaxialtransmission line of the type shown in Fig. of-'the above-mentionedClogston application and in'wliich'WaYQSiof vario 1s modes are excitedin accordance Wiih .INCDH i v i Y l v "Figs, 2A to 2E, inclusive, showapproximate current densi, ypattern's of theffundamental, second, third,fourth andiifth Qdes, respectively, in a transmission line of in Fig, 2;'Figsg andtare end views of composite conductors of theftypes:showninFi'gs. 18A and 18B, respectively, of the v above-rnentionedClogston application and in which waves operatingjinf` the modes shownin Figs. 2A to 2E, inclusive,:canbefpropagated in accordance with theinven- 5, 6`an l ,7v are longitudinal sectional views, with portions',brokenv away, of a composite conductor of the type, shownmin Fig.y 1 andinputand output terminal connectionstherefor for exciting therein andremoving therefrom wavesfoperating inthe principal mode, second andthirdmodes', and fourth and fth modes, respectively;

Figs', 8, 9 andnl()y are longitudinal sectional views, with portionsbroken'away, of acomposite conductor of the type'shownwin Fig,7 2 andinput and output terminal connections therefor for exciting therein andremoving therefrom wavesoperating in the principal mode, second mode,and third mode, respectively; and

Fig. 1l is a schematic diagram of a composite conductor of the typeshown in Fig. 2 and circuit connections for applying thereto andremoving therefrom simultaneously and independently a plurality of modespropagating in different modes.

Referring more particularly to the drawings, Fig. l shows, by way ofexample for purposes of illustration, a conductor 30 in which, inaccordance with the invention, various waves operating at differentmodes can be propagated. The conductor 30 comprises a central core 31(which may be either of metal or dielectric material), a cylindricalinner conductor or stack 32 formed of many laminations of metal spacedby insulating material, a cylindrical outer conductor or stack 33similarly formed cylindrical outer conductor or stack 33 similarlyformed of a multiplicity of layers of metal spaced by insulatingmaterial and separated from the inner conductor 32 by an annulardielectric member 34, and an outer sheath 35 of metal or other suitableshielding material. As disclosed in the above-mentioned Clogstonapplication, the metal layers in the composite conductors 32 and 33 areeach very thin compared to the skin depth of theV conducting materialbeing used, which, for example, can be copper, silver or aluminum. Theinsulating layers in the compositerconductors 32and 33-are also madevery' thin and may-befof any suitable material. Preferably, they are ofthe order of one-half the thickness of each metal layer although this isnot necessarily true in all cases. The inner-conductor 32 has perhaps l0to 100 or more metal layers and the outer conductor 33 has a somewhatsimilar number of metallic layers although there need not beexactly-.the same number as in the inner conductor 32. Sincethere are alarge number of insulating and metallic layers, it makes no differencewhether the rst or the last layer in each stack (32 or 33) is of metalor of insulation. For a wide band of frequencies, the dielectricmaterial 34is preferably chosenV so that Vthervelocity of propagation ofa wave going down the length of the conductor hasthe proper value togive minimumattenuation, asset forth in the above-identified Clogstonapplication. Equation Z'g-iven above sets forth `the relationshipbetween el, which is the dielectric constant of the member 34, and` e2,which is the dielectric constant of the insulating material in thestacks32 and-33, in terms of the thickness W of the metal laminae and of thethickness t of the insulating material therebetween. For a more detaileddescriptionof theconductor shown in Fig. l, reference is made to thedescription in the above-identified Clogston application, specialreference being made to Fig. 7B.

As =pointed outabove, there can be set up in the conductor 30simultaneously and independently electromagnetic waves propagating inrespectively different conduction current modes. Figs. 1A to 1E,inclusive, show ,i approximate, typical patterns of a fundamental mode(Fig. 1A), a second order mode (Fig. 1B), a thirdiorder mode (Fig.V 1C),a fourth order mode (Fig. 1D), and a iifthorder .mode (Fig. 1E.)Whiletherezis, a .large number of modes that can be transmitted in aconductor suchas thatshown in Fig. l, actually, as a practical matter,.only a moderate number of thelower orderV modes will be used due to thefact that the attenuation of the higher modes is muchhigher thanthat ofthe fundamental and increases as the order of mode increases. In each ofFigs. lAtol 1E, inclusive, the horizontal dimension represents currentdensity while the vertical .dimension represents radial distance, theoverall distance `shown-as 2din the `drawing being equal to the` overalldistance between the inside surface of the shield 35 andthev outsidesurface of the core 31. It willbe noted that the fundamental (Fig. 1A),the third order mode (Fig. 1C) and the fifth order mode (Fig. 1E) havean odd order symmetry with respect to the vertical center line whereasthe curves forthe second and fourth order modes (Figs. 1B. and,lDv)-have evenorder symmetry with respect to this vertical centerline,The modes shown in Figs. 1A

t6 l, inclusive. transmit successively broader frequency bands, and`this factor can be utilized in multiplexing.

l Fig. 2 is a longitudinal view with portions broken away of a cable 30Alike that shown in Fig. 1 except that the space occupied by thecylindrical dielectric member 34 of the conductor 30 in Fig. 1 islledtup with insulated laminations so that, in eifect, the members 33,34 and 32 of the conductor 30 are replaced by a single cylindrical`stack 36 of alternate metal and insulating laminae of the same generaldimensions as those in the conductor 30. For a more detailed description`of the conductor shown in Fig. 2, reference is made to theabove-identified Clogston` application with specific reference to Fig.17A.

Figs. 2A to 2E, inclusive, show mode patterns for the conductor 30A forthe fundamental mode (Fig. 2A), the second order mode (Fig. 2B), thethird order mode (Fig. 2C), the fourth order mode (Fig. 2D) and thefifth order mode (Fig. 2E). In each case, the mode numbers are indicatedby the number set equal to n in the drawing.

The modes of Figs. lA to 1E, inclusive, can now be compared to Figs. 2A`to 2E, inclusive, respectively.

i Clearly, there is a one to one correspondence of the modes since thepartially filled conductor 30 of Fig. l can be made to approach thecompletely filled conductor 30A of Fig. 2 continuously by adding morelaminated material. The correspondence can be seen by comparing Fig. 1Ato Fig. 2A, Fig. 1B to Fig. 2B, Fig. 1C to Fig. 2C, Fig. 1D to Fig. 2Dand Fig. 1E to Fig. 2E.

Figs. 3 and 4 are end views of composite conductors 30B and 30C similarto conductor 30A in Fig. 2 except that instead of laminations amultiplicity -of tiny iilaments 40 of diameter small compared to a skindepth are used. Fig. 3 differs from Fig. 4 in that a central core 41 isernployed and each of conductors 30B and 30C utilizes an outer shield 42corresponding `to the shield 35 of Figs. 1 and 2. The metal filaments40are spaced by insulating material 43. For more detailed descriptionsof the conductors 30B and 30C reference is made to the aboveidentifiedClogston application with special reference to Figs. 18A and 18B,respectively. The mode patterns of the conductors 30B and 30C are likethose for the conductor 30A of Fig. 2 so will not be repeated. Thevarious modes can be set up in the conductors 30B and 30C in a mannersimilar to that which is used in propagating the waves in the conductor30A to be described below. p Figs. 5, 6 and 7 illustrate means forapplying and removing electromagnetic waves propagating in thefundamental, second and third modes, and fourth and fth modes,respectively, in a conductor 30 of the type shown in Fig. 1, that is, acable of the partially filled type. It is to be understood that in eachof Figs. 5, 6 and 7 the conductor 30 may be a cable of relatively greatlength such as, for example, of the order `of miles, or it may berelatively short (a matter of inches or feet). Each end of `the cable 30is terminated by butting it against a ,coaxial cable 50 having an innerconductor 51 in contact "with the inner conductor 31, an outer conductor52 in contact with the outer shield 35 and dielectric member 53completely filling the space between the conductors 51 and 52 and havinga value of dielectric constant equal to that given in the expression forel given in Equation 2 above. `If the central core 31 of the cable 30 isof dielectric rat-her than of metallic material the conductor 51 is madelarge enough or the end thereof near the conductor 30 enlarged to suchan extent that contact is made to at least one of the metal laminae inthe inner composite conductor 32. A source 60 of signal voltage (whichmay comprise a wide band of frequencies or a :single frequency of highor low value) is applied between the outer and inner conductors 52 and51 ofthe input 4cable 50 and waves operating in the fundamental mode,are propagated in the cable 30 and assume the space pattern shown inFig. 1A. These waves of the fundamental mode can be removed from theoutput cable 50 by connecting a utilization device 61, sch as the inputresistor of a suitable amplifier, for example, between the conductors5-1 and 52 of this cable;

lFig. 6 shows an arrangement wherein' the second and third order' modes(Fig. 1B) are set up in the conductor 30 and removed therefrom. Theinput and output cables 50A are like the cables 50 of Fig. 5 except thatthey have two annular rings 54 and 55 placed to contact the innermostlaminae of the stack 33 and the outermost laminae of the stack 31,respectively. Each annular ring is wide compared to a skin depth. A rstsource 62 is applied between the ring 55 and the inner conductor 51 ofthe input cable 50A While a second source 63 is applied between theouter annular ring 54 and the outer conductor 52 of the cable 50A. Withuse of the proper phase and magnitude of the voltage of the source 62with respect to that of the signal of the source 63, the mode shown inFig. 1B (called the second mode) or that shown in Fig. 1C (called the3rd mode) can be established. These signals can be removed from thecable 30 by means -of the righthand or output cable 50A (by connectingsuitable utilization devices 64 and 65 to the members of the right-handca'ble 50A similar to the connections for the sources 62 and 63 to theleft-hand cable 50A). It will -be readily apparent that two entirelydiifeent signals can be sent in the arrangement of Fig.

The arrangement shown in Fig. 7 is similar to that shown in Fig. 6except that four annular rings 56, 57, 58 and 59 are used in the inputand output cables 50B instead of the two rings 54 and -55 inthe cables50A of Fig. 6. The ring 56 contacts substantially the center of thestack 33, `the ring 57 contacts the lower portion of stack 33, the ring58 contacts the upper portion of the stack 32, and the ring 59 contactsthe middle portion of stack 32; The source 66 is applied between theannular ring 59 and the inner conductor 5'1 of the input cable 50B. Thisconductor 51 is also connected to the annular ring 58. The source 67 isconnected between the outer conductor 52 of the input cable 50B and theannular ring 56, the ring 57 being also connected to the conductor 52.By means of this arrangement, wave shapes of the type shown in Fig. 1Dor Fig. 1E, in any proportion, canbe obtained by varying the phase andamplitude of the signal source `66 and 67. Utilization devices 68 and 69connected to the output cable 50B similarly to the way in which thesourcjes 66 tnd 67 are connected to the input cable`50B can e use toremove the Waves a lied end of the cable 30. pp to the Input Figs. 8, 9and l0 show arrangements in connection with the conductor 30A of Fig. 2for launching and removing electromagnetic waves propagating in themodes shown in Flgs. 2A, 2B and 2C, respectively. The input and outputcables 50 are similar to the input and output cables 50 shown in Fig. 5,the dielectric member 53 having a dlelectric constant which is equal tothe average dielectric constant of the stack 36 of the cable 30A. Thesource 70 applied between the conductors 51 and 52 excites a waveoperating at the fundamental mode and this wave is removed from thecable 30A by connecting the utilization device 71 between the conductors51 and 52 of the output (right-hand) cable 50. Fig. 9 shows anarrangement for exciting a wave operatmg in the second order mode shownin Fig. 2B. This arrangement employs two cables 50C connected to respecftively opposite ends of cable 30A. Each cable 50C is like the cable 50except that it has `an annular ring 72 therein substantially in themiddle of the stack 36 of the cable 30A. To Cause the excited wave topropagate in the second order mode as shown in Fig. 2B, the source 73 isconnected between the inner conductor 51 of the cable 50C and theannular ring 72 thereof, the outer conductor 52 being also connected tothe inner conductor 51. To remove this wave from the conductor 30A, asuitable utilization device 74 is connected to the output cable 50C in amanner similar to th econnection of the source 73 to the input cable50C.

Fig. l shows an arrangement for utilizing a wave propagating in thethird order mode as `shown in Fig. 2C in the cable A. The input andoutput cables 50D lare connected to the respective ends of the cable30A, and these cables are similar to cable except that two annular ringsand 76, respectively, are placed in contact with 4the axis from stack 36so as toV divide the space between the inner terminal 51 and the outerterminal 52 approximately into thirds. Terminal 78 of the source 77 isconnected to the ring 75 and to the inner conductor 51, while terminal79 of the source 77 is connected to the outer conductor 52 and the ring76. The utilization device 80 is connected' to the output cable 50D in amanner similar to that in which the source 77 is connected to the inputcable 50D.

In -all of the arrangements described above, the annular rings in thecables 50A to 50D inclusive, preferably have a thickness which isseveral times skin thickness. Also with respect to Figs. 8 to l0,inclusive, cables of the type shown in Figs. 3 and 4 can be used inplace of the cable 30A, the input and output cables being similar tothose used with the cable 30A.

Fig. ll shows an arrangement for multiplexing using a v plurality ofmodes simultaneously and independently. A

signal source for the dominant mode is applied to the primary winding 91of the transformer 92, the output winding of which is split up into anumber of coils, for example, 1-2, 2--3, 3-4, 5 6 11-12. Another signalsource 93 is connected to the input winding 94 of the second transformer95 having a multiplicity of separated windings 1--2, 3--4 23-24. Thesecondary windings of the transformers 92 and 95 are connected as shownin the drawing to the outer and inner terminals 35 and 31 respectively,of a conductor 30A and to a multiplicity of metallic annularrings 101,102, 103, 104, 105, 106, 107, 108, 109, therebetween, each annular ring101, 102, etc. being7 wide enough to contact the ends of a plurality ofmetal laminae in the stack 36. The various 4secondary coils are Wrappedto produce current in the annular rings in the proper relativedirections as indicated in the full line arrows for the dominant modecurrent and the dotted line arrows for the second mode current.- It willbe noted that the connections are made in such a manner that the properphase reversals are obtained so that a signal of the dominant mode andalso one of the second order mode are propagated simultaneously in thecable 30A and also due to the arrangement of windings (that is, theeiect of one winding is to cancel out the other in certain instances),none of the dominant mode signal appears in the primary winding of thetransformer 95 and none of the second order mode signal appears in theprimary mode winding of the transformer 92. Similarly, a signal sourcefor the third order, or higher mode, can be connected to the cable 30Athrough transformer 120A in a manner which will be obvious to oneskilled in the art in view of the circuitry for transformers 92 and 95.The transformers 121, 122, 123, etc., respectively, connected toutilization devices 124, in a mannersimilar toV the connection of thesignal sources 90, 93 and 120 in the input end are used to remove thesignals operating at the various modes.

It is'obvious that the arrangement of Fig. ll can be used with aconductor 30 of Fig. l, the connections above the dotted line beingapplied to annular rings for the outer stack 33 and those below thedotted line 130 being applied to rings for the inner stack 32. Moreoverthe arrangement ofFig. l1 is applicable without change to conductorsofthe types shown in Figs. 3 and 4.

Although it is theoretically possible to determine by mathematicalanalysis the proper relative turns ratios among the diferentwindingscomprising each mode transf ormer, in practice it is simpler and betterto'determine this experimentally. A length of laminated cable issuccessively excited (asI in Figs. 8; to l0, inclusive) toeach mode ofinterest in turn. At the other end which may be open (high impedancetermination) annular rings (such as rings 101 to 110 of Fig. ll) areutilized and form a xed excitation at the sending end, the voltages ofinterest are measured with a high impedance voltmeter. The number ofturns on the input winding is so adjusted that this winding presents thedesired impedance to the signal source. If it is desired to keep thelength of cable tot a minimumthe above experimental determination can becarried out by using the cable as a half-wavelength resonator. In thiscase, the sending end termination is also of very high impedance whichmeans the exciter (cable 50; 50A etc.) is very loosely coupled to thecable.

The invention has a number of advantages. For example, even though thehigher modes are attenuated more rapidly than the fundamental mode, theinvention is useful in an arrangement where a signal cable of type 30 or30A, for example, exists (and it is not practical to install anotherone) when it is desired' to send one or more additional signalsindependently and simultaneously with therst; Another advantage lies inthe fact that a conductor operating at the higher modes will transmit awider frequency band than when operated at the l'ower order modes, thusproviding more channels than the dominant mode.

It is obvious that the invention is not restricted to the specificarrangements shown as obviously other mod-ifications can be made in theembodiments described abjove without departing from the scop'e of the'invention as indicated in the claims.

What is claimed is:

1.- In combination, a composite electromagnetic wave conductorcomprising amultiplieity of elongated conducting portions separated byinsulating material, said conducting and insulating portions being sodimensioned relative to each other andthe rdielectric constant of theinsulating material being such that the conductor can propagate aplurality of conduction current modes of different order, means forapplying to said conductor electromagnetic waves propagating in aconduction current mode of a higher order than theA principal one, andmeans for utilizing the waves of said higher order mode.

2. In combination, aV composite electromagnetic wave conductorcomprising a multiplicity of concentric layers of conducting materialseparated by insulating material and in which all of the layers withinthe composite conductor are substantially evenly spaced from adjacentones, said conducting layers and said insulating'material being soproportioned relative to each other and the dielectric constant of theinsulating material being such thatthe conductor can propagate aplurality of conduction current rnodesof different order, meansv forapplying to said conductor electromagnetic waves propagating in aconduction current mode of a higher order than the principal one, andmeans for utilizing the waves of said higher order mode.

3. In combination, amedium for the transmission of electromagnetic wavescomprisingV two coaxially arranged composite conductors separated bydielectric material,` each` composite conductor being circular in crosssection and each comprising'a composite stack of insulated concentricthin-walled conducting cylinders, said conducting cylinders and theinsulation being so `dimensioned and the dielectric constant of theinsulating material being such that the medium can propagate a pluralityof conduction current'modes of different order, means for applying tosaid medium electromagnetic waves propagating in a conduction currentmode of a higher order than theA principal one, and means for utilizingthe wavesof saidhigher order mode.

4. In combination,l a cable comprising ay central wall and an outershelland means between thewall andthe shell for the conduction of current,said means comprising a multiplicity of very thin conducting layersseparated by very thin insulated layers, said conducting and insulatinglayers being so dimensioned and the dielectric constant of theinsulating layers being such that the cable can propagate a plurality ofconduction current modes of different order, means for applying to saidcomposite conductor electromagnetic waves propagating in a conductioncurrent mode of higher order than the principal one, and means forutilizing the waves of said higher order mode.

5. In combination, a composite electromagnetic wave conductor comprisinga multiplicity or elongated metallic laments spaced by insulatingmaterial, said laments being so dimensioned and the dielectric constantof the insulating material being such that the conductor can propagate aplurality of conduction current modes of different order, means forapplying to said conductor electromagnetic waves propagating in aconduction current mode of a higher order than the principal one, andmeans for utilizing thewaves of said higher order mode.

6. In combination, a composite electromagnetic wave conductor comprisinga multiplicity of elongated conducting portions spaced by insulatingmaterial, said conducting and insulating portions being so dimensionedrelative to each other and the dielectric constant of the insulatingmaterial being such that the conductor can propagate a plurality ofconduction current modes of different order, means for applying to saidconductor simultaneously and independently electromagnetic wavespropagating in different order conduction current modes, and means forutilizing any of said waves to the exclusion of any other one.

7. In combination, a composite electromagnetic wave conductor comprisinga multiplicity of elongated conducting portions spaced by insulatingmaterial, said conducting and insulating portions being so dimensionedrelative to each other and the dielectric constant of the insulatingmaterial being such that the conductor can propagate a plurality ofconduction current modes of different order, means for applying to saidconductor simultaneously and independently electromagnetic wavespropagating in different order conduction current modes, and means forutilizing all of said waves independently.

8. In combination, a composite electromagnetic wave conductor comprisinga multiplicity of elongated conducting portions spaced by insulatingmaterial, said conducting and insulating portions being so dimensionedrelative to each other and the dielectric constant of the insulatingmaterial being such that the conductor can propagate a plurality ofconduction current modes of different order, means for applying to saidconductor electromagnetic waves propagating in the principal mode, meansfor applying to said conductor electromagnetic waves propagating in aconduction current mode of a higher order than the principal one, andmeans for removing said waves of the principal mode and of said higherorder mode from said conductor independently of one another.

9. The combination of elements as in claim 8 in which said applyingmeans and removing means comprise transformer means.

10. A wave transmission system comprising a composite electromagneticwave conductor including a multiplicity of elongated conducting portionsseparated by insulating material the thickness of each conductingportion being less than the skin depth of penetration of waves at thehighest frequency of operation of said system, the thickness of theinsulating material between the conducting portions being soproportioned relative to the conducting portions and the dielectricconstant of the insulating material being such that the conductor canpropagate a plurality of conduction current modes of different order,means for applying to said conductor electromagnetic waves propagatingin a conduction current mode of a higher order than the fundamental one,and means for utilizing the waves of said higher order mode.

11. A wave transmission system comprising a composite electromagneticwave conductor capable of propagating a plurality of conduction currentmodes of different order and having a multiplicity of elongatedconducting portions separated by insulating material, there being asuflicient number of conducting portions to carry a signicant fractionof the total current, the thickness of each of said conducting portionsbeing less than a skin depth of penetration of the highest frequency ofoperation of said system, means including said conducting portions andsaid insulating material for causing the propagation velocity of anelectromagnetic wave in said conductor to be susbtantially uniformacross the cross-sectional area of the conductor, means at one end forapplying to said conductor electromagnetic waves propagating in aconduction current mode of a higher order than the fundamental one, andmeans at the other end for utilizing the waves of said higher ordermode.

l2. A wave transmission system comprising a composite electromagneticwave conductor capable of propagating a plurality of conduction currentmodes of different order and having inner and outer conducting membersand a multiplicity of elongated conducting portions separated byinsulating material between said inner and outer members, there being asuflicient number of conducting portions to carry a significant fractionof the total current, the thickness of each of said conducting portionsbeing less than a skin depth of penetration of the highest frequency ofoperation of said system, means including said conducting portions andsaid insulating material for causing the propagation velocity of anelectromagnetic wave in said conductor to be susbtantially uniformacross the cross-sectional area of the conductor, means at one end forapplying to said conductor electromagnetic waves propagating in aconduction current mode of a higher order than the fundamental one, andmeans at the other end for utilizing the waves of said higher ordermode.

13. A wave transmission system as claimed in claim 1l wherein the meansfor applying electromagnetic waves to the conductor comprises a sourceof signal voltage and means connecting said source to the innerconducting member and to at least one of said elongated conductingportions which lies intermediate the inner and outer conducting members.

14. A wave transmission system as claimed in claim 13 wherein the meansconnecting the source comprises a coaxial cable having inner and outerconducting members contacting the inner and outer conducting members ofthe composite conductor and an intermediate conducting member contactingat least one of said conducting portions, said source being electricallyconnected to the inner and intermediate conducting members of saidcoaxial cable.

References Cited inthe le of this patent UNITED STATES PATENTS 1,701,278Silbermann Feb. 5, 1929 1,855,303 McCurdy Apr. 26, 1932 2,088,749 KingAug. 3, 1937 2,129,711 Southworth Sept. 13, 1938 2,191,995 Scott f. Feb.27, 1940 2,231,602 Southworth Feb. 11, 1941 2,257,783 Bowen Oct. 7, 19412,267,289 Roosenstein Dec. 23, 1941 2,676,309 Armstrong Apr. 20, 1954OTHER REFERENCES Microwave Transmission Design Data, Sperry GyroscopeCo., Publications Dept., Great Neck, Long Island, page 7. (Received inPatent Office Library Feb. 18, 1946.) Copy in Div. 69.

